From the prospectus (March 2000 edition) entitled “Crane Construction Kit KBK classic and KBK ergo” of the firm Demag Cranes & Components GmbH, Wetter, Germany, there is known a crane construction kit system with C-shaped and I-shaped rails which are open at the bottom, by which one can implement different kinds of constructions, such as monorail telphers and single and double-beam overhead cranes. In each case, the rails are suspended from support structures, other rails, or traversing gears which run into other rails. These suspension systems have a pendulum type design, which ensures that the rails align themselves and thus come into a state of equilibrium, i.e., no significant bending load occurs in the tension element. The pendulum suspension occurs through ball and socket bearings, having steel ball segments and mating ball cups with plastic slide shells. The ball segments are fastened to the end of a compound tension element. Thus, the tension element for the most part consists (looking down from above) of a lug to fasten the tension element to the supporting structures, other rails or traversing gears, and a shaft joined to it as a single piece, on which the ball segment is screwed and secured.
In a suspension system of C-shaped rails open at the bottom, with a web broadening out toward the top and arranged at the top side of the rail, preferably a Y-shaped or T-shaped web, the fixing device consists of two identical fixing parts. These fixing parts are formed as sheet metal parts in such a way that, after being fitted together and held by screws, the broadening web of the rail is clamped in the lower region and the ball cup is accommodated in the upper region, while the tension element is passed through an opening.
This type of suspension system has been popular for many years and is easily installed on any given portion of a rail, since the fixing parts are fitted together there and tightened together by the screws for clamping against the rail.
From US 2004/0238473 A1 there is known a crane arrangement in which a bridge girder can run on parallel rails that are spaced apart from each other by means of traversing gears arranged at its ends. The bridge girder is clamped together with the traversing gears by U-shaped stirrups, open at the bottom, which enclose the bridge girder. Between the stirrups and the traversing gears, there are vertically-oriented ball and socket bearings, so that the traversing gears can turn 360 degrees about a vertical axis relative to the bridge girder and can also be tilted laterally. The ball and socket bearings have balls made of steel and cups of nylon.
In these ball and socket elements, the ball of the tension element must be introduced into the ball cup, while the shaft passes through the central bore of the cup. Therefore, the tension elements are made of at least two parts, namely, a tension rod and a ball head, which are fastened to each other after being assembled with the tension rod introduced through the central bore in the ball cup. One often uses ball nuts that are screwed onto the tension rod. This connection is secured, for example, by a cotter pin.
However, this design of the tension element can only fulfill the load requirements placed on the tension element by an overdimensioning. Furthermore, the parts of the above ball and socket unit have to be appropriately machined or fabricated in order to enable their connection.
In addition, the ball cups can be ruined by improper use or deficient maintenance, which results in increased friction between ball head and ball cup. In the case of two-part tension elements made from a tension rod and ball head, the element securing the connection between tension rod and ball head is then overloaded. This can result in collapse of the bridge girder. The securing element can also fail, which likewise results in a failure of the suspension. Furthermore, the tension rod is weakened by the notch effect of the thread placed on it. Moreover, when the load is removed from the rail, the rail lifts slightly and the ball cup is pulled off from the ball head. When the rail is then placed under load, there is an abrupt loading of the ball and socket joint, which also has to be factored into the design.
Moreover, suspension systems are known from the firm Ingersoll Rand Zimmerman, Milwaukee, USA (see, for example, www.irtools.com/_imgLibrary/complete/Zimmerman_HaengerAjc—1.jpg). The suspension system includes a C-shaped crane rail open at the bottom, having a Y-shaped web broadening at the top, which is arranged on the top side of the rail for a fixing unit made of two identical fixing parts. This suspension system has a tension element consisting essentially of a tension rod and a lug. The tension rod is mounted in the lug by its lower end, able to turn about a vertical axis, and secured rigidly to a supporting structure at its upper end. The lug, in turn, is fastened by its bore to a bolt, extending in the lengthwise direction of the rail. Thus, the tension element can swivel transversely to the rail and can turn about a vertical axis. The tension element is rigid in and against the lengthwise direction of the rail. Furthermore, the bolt for the lug is mounted in the fixing parts. The fixing parts can swivel about the bolt and restrain a Y-shaped web by means of screws. The screws are led through a borehole in the web.
Also known from the firm Krantechnik Müller, Lebach, Germany, are additional suspension systems for the above-described C-shaped crane rails, open at the bottom, with the Y-shaped broadening web. These consist essentially of a tension element, a pivoting bearing, a bolt, a bracket and a fixing device. The tension element has one borehole at each its upper and its lower end, each of which receive a pivoting bearing with a ball cup and a ball head. The ball head is connected to the bolt, which extends in the lengthwise direction of the rail. The ends of the bolt extending in front of and behind the ball head are each secured in pivoting manner and by a cotter pin in the legs of a U-shaped bracket, open at the top, whose web extending below and at a distance from the bolt is accommodated by the fixing device with the Y-shaped web. The fixing device consists of two identical fixing parts, which are fastened by screws to clamp against the web of the bracket and the Y-shaped web of the rail. Use of the bracket results in a large structural height. The pivoting mounting of the ends of the bolt in the legs of the bracket results in wear on the boreholes of the bracket.
European patent application EP 0 860 394 A2 describes the fastening of a tension element with a ball head in a mating ball cup by a fixing device on a Y-shaped web of a rail. The fixing device could be a one-piece device. The ball head of the tension element is led from above through the appropriately dimensioned opening of the fixing device and then the two-piece ball cup will likewise be introduced through this opening from the side. Whether the fixing device is secured by further means to the Y-shaped web of the rail is not specified.
German patent application DE-A 51 096 288 shows a fixing device for suspending a rail from an I-shaped beam. This C-shaped fixing device, open on top, has two opposite and swiveling gripping arms which, after the fixing device is arranged underneath the web of the rail, are swiveled by their hook-like ends into a fixing position on the top side of the web. The gripping arms are each fixed by a screw in the fixing position. In particular, this type of fixing is distinguished by the possibility of adjusting the fixing system with regard to the I-shaped rail. Even in the fixing position of the gripping arms, there is sufficient lateral play to adjust the screws and move the fixing device itself sideways in relation to the rail. This document does not discuss preventing a collapse caused by failure of the screws.
Moreover, there is known from German patent DE 197 53 169 C2 a device for suspending a rail, especially a hollow rail open at the bottom for an overhead crane. Here, the rail also includes a Y-shaped web arranged on top, being enclosed by a C-shaped fixing device, which is suspended via a ball head and a tension element from an I-shaped rail. The fixing device between the ball head and the Y-shaped web is in two pieces and is joined together by two screws extending transversely to the rail, and arranged one behind the other in the lengthwise direction of the rail. Thus, the ball head is grasped by the two parts of the fixing device. A failure of the screws would result in a loosening of the fixing parts, thus releasing the ball head of the tension element.
Moreover, a device for suspending the rails of a rail system for an overhead crane is known from DE 101 15 565 C2, having elastic damper elements in the region where the ball heads are supported.